1. Field of the Invention
This invention generally relates to optical lens modules, and more specifically, to a piezoelectrically driven optical lens module.
2. Description of Related Art
In order to cope with the trends toward small-sized cellular phones and cameras, optical systems and their actuators applied to cellular phones and cameras nowadays tend to have a simple structure and a small size. A piezoelectric actuator, which has advantageous features of small size, high output force, low power consumption, noiselessness, and high compatibility, has been widely applied to digital cameras and camera phones, for driving an optical lens module to zoom in or out, and has also become one of the important techniques applied to optical systems or related merchandises.
Taiwanese Patent No. 589,777 discloses a multi-layered, thin-disk, piezoelectrically driven ultrasonic motor, which is characterized by applying high AC voltages to piezoelectric buzzers, to produce deformation of alternate expansion and contraction. Consequently, an elastic vibration element is driven to produce traveling and stationary waves to provide external kinetics, and form a driving module in a vertical or horizontal mode. Although the wear and tear of the components is reduced, the patent requires using multiple driving modules in combinations. Thus, the motor structure is complicated, and miniaturization is impossible.
Referring to FIG. 1, U.S. Pat. No. 7,099,093 discloses a compact lens module comprising a plurality of driving units 100 for driving a contact wheel 101 to move a plurality of shafts 102, and further enabling a plurality of lenses 103 to move forward or backward. By applying the torque principle (M=r×F), downsizing a plurality of contact wheels 101 reduces the overall volume of the compact lens module. However, it requires the driving units 100 to output more force, thereby consuming more power and decreasing overall driving efficiency; on the other hand, enlarging the contact wheel 101 increases the overall volume of the compact lens module to the detriment of miniaturization.
Referring to FIG. 2, U.S. Pat. No. 5,225,941 discloses a driving device characterized by a laminated piezoelectric element 104, a plurality of leaf springs 105, and a plurality of lenses 106. The piezoelectric element 104 functions as a power source and leaf springs 105 generate pre-load. When a signal is inputted, the leaf springs 105 cause a plurality of lenses 106 to move forward or backward. However, the piezoelectric element 104 has to be implemented in the form of a multi-layered piezoelectric disk to perform sufficient displacement and generate sufficient output force, and therefore, it is difficult to thin out the laminated piezoelectric element 104.
U.S. Pat. No. 6,710,950 discloses a piezoelectric actuator applied to an optical system of digital cameras. As shown in FIG. 3, a piezoelectric actuator 109 is coupled to a lens barrel 108 housing a lens element 107. The piezoelectric actuator 109 comprises a circuit board 110, a plurality of piezoelectric elements 111, and a plurality of engagement pads 112. The circuit board 110 and each the piezoelectric elements 111 are disposed on the inner surface of the circuit board 110 at an interval, and the engagement pads 112 are coupled to the surface of each of the piezoelectric elements 111. Then, a voltage is applied to the piezoelectric elements 111 circumferentially disposed on the periphery of the lens element 107 to generate surface waves, thereby enabling each of the engagement pads 112 to simultaneously poke the lens element 107 to displace axially relative to the lens barrel 108, and further achieving the objects of zooming or focusing of the optical lens of a digital camera. However, a plurality of piezoelectric elements is used in the patent, thereby incurring high costs and causing difficulty in assembly. Moreover, it is very difficult to control precision of displacements, while driving each of the piezoelectric elements to simultaneously poke the lens element. Furthermore, the length of the lens barrel 108 depends on displacements, and thus the length of the lens barrel 108 increases as the distance of a displacement increases. This is detrimental to miniaturization.
U.S. Pat. No. 6,961,193 discloses a driving device for driving a lens. As shown in FIG. 4, the driving device comprises a driving means 113 for generating inertia to drive a lens 114 to move forward or backward. However, a weight 115 is externally applied to produce inertia. This does not only increase the overall external diameter of the driving device and difficulty in assembly, but also increases the overall weight of the driving device.
In view of above-mentioned drawbacks of the prior arts, it is important to provide a piezoelectrically driven optical lens module with advantageous features, such as large torque, a small size, simplified constituent elements, rigid framework, ease of fabrication and assembly.